Janus structure design of polyimide composite foam for absorption-dominated EMI shielding and thermal insulation

In the present work, by virtue of the synergistic and independent effects of Janus structure, an asymmetric nickel-chain/multiwall carbon nanotube/polyimide (Ni/MWCNTs/PI) composite foam with absorption-dominated electromagnetic interference (EMI) shielding and thermal insulation performances was successfully fabricated through an ordered casting and directional freeze-drying strategy. Water-soluble polyamic acid (PAA) was chosen to match the oriented freeze-drying method to acquire oriented pores, and the thermal imidization process from PAA to PI exactly eliminated the interface of the multilayered structure. By controlling the electro-magnetic gradient and propagation path of the incident microwaves in the MWCNT/PI and Ni/PI layers, the PI composite foam exhibited an efficient EMI SE of 55.8 dB in the X-band with extremely low reflection characteristics (R=0.22). The asymmetric conductive network also greatly preserved the thermal insulation properties of PI. The thermal conductivity (TC) of the Ni/MWCNT/PI composite foam was as low as 0.032 W/(m K). In addition, owing to the elimination of MWCNT/PI and Ni/PI interfaces during the thermal imidization process, the composite foam showed satisfactory compressive strength. The fabricated PI composite foam could provide reliable electromagnetic protection in complex applications and withstand high temperatures, which has great potential in cutting-edge applications such as advanced aircraft.